To enhance the performance of electric double layer capacitors(EDLCs), we attempted to improve electrode and electrolyte material drastically. As a result of the effort, we have got fruitful achievement as follows :A gel electrolyte based on PVdF-HFP has been applied to EDLCs. Technical renewal, i.e., an extremely thin gel electrolyte film(thickness : ca.10μm) and the optimization of electrode-electrolyte interface junction, successfully provided prominent EDLC performance. Especially, when an extremely high rate charge-discharge current was applied to the present gel EDLC, no decrease in discharge capacitance was observed while the corresponding EDLC with a conventional organic electrolyte showed a decrease in the capacitance. This result is noteworthy because our gel EDLC is very thin as described above and contains usual activated carbon sheet electrodes.We have also attempted to improve electrode material for EDLCs. The exposure of activated carbon electrode to cold plasma generated from fluorinated or alkoxysilane gas induced the generation of surface functional groups and the optimization of pore size distribution at an electrode interface. This modification enhanced the rate capability of the carbon electrode. Furthermore, we applied "carbon nanotube sheet", carbon nanotubes oriented vertically on an aluminum foil like carpet pile, to an EDLC electrode. It was found that the carbon nanotube sheet electrode is suitable for a high rate cycling ; the electrode can provide a high capacitance even with a high current in so much that the capacitance of an EDLC with usual activated carbon electrodes becomes zero.In addition, we tried to apply some of the above-mentioned technologies to rechargeable lithium battery systems.